Portable keyboards associated with computers and especially word processing equipment can be damaged by spilled liquids and dust and other harmful vapors in the air.
Some keyboard manufacturers make available vacuum formed sheet plastic covers which can be placed over the keyboards. Some of these covers are sufficiently flexible to permit the keyboard to be used with the cover in place; others must be removed before the keyboard can be used. Such covers do not provide a hermetically sealed environment for the keyboard and, of course, provide no protection at all when removed to permit use of the keyboard.
Furthermore, keyboards are produced in a variety (literally hundreds) of different configurations. Thus, an equal number of the vacuum formed covers would be required to provide protection for all the different keyboards which are available now or in the future. This greatly complicates the manufacture and distribution of keyboard covers.